Imagine being able to effortlessly track your fitness routine without having to look away or even think about it. Bosch Sensortec GmbH (Reutlingen/ Kusterdingen, Germany) has developed a “Light Drive” system to display data from fitness and navigation sensors onto a lens of a pair of smart eyeglasses that have transparency comparable to normal eyeglasses and that are comfortable enough to be worn all day. The data image is projected directly onto the wearer’s retina so that it is always in focus and readable despite changing ambient light conditions. You can get feedback while jogging, stair-climbing, exercising, or bike-riding.

The Light Drive can interface with any Bluetooth-enabled device such as a smart-phone or fitness tracker. According to Dr. Lucas Ginzinger, Head of Product Area Optics, Bosch Sensortec, in the future the connection may be via 5G.

How it Works

The components of the Light Drive are shown in Figure 1. The working principles are illustrated in Figure 2.

The Bluetooth input data is transferred to a dedicated ASIC controller. It, in turn, controls the laser module, which consists of three colors of laser diodes: red, green, and blue. The three beams they produce are aligned and merged into a single beam. The controller modulates the laser beam by switching colors off and on, thereby painting a picture. The modulated laser beam is focused onto a set of MEMS mirrors. These mirrors are actuated by the system controller to project the beam onto a holographic film molded into the lens and to scan the image one line at a time. The film acts like a mirror that only reflects the three wavelengths of the laser beam. All other light passes through it. Although in principle, the functionality is like a mirror, because the mirroring function is so limited, you still have 99% transparency. That is done by what is called a volume-holographic film, which is a micrometer in thickness.

Figure 2. Light Drive working principles. (Image courtesy of Bosch Sensortec)

The unique feature of the Light Engine is that the image produced by the laser beam is reflected by the nearly invisible holographic film directly into your pupil. So, the image is created on your retina, not inside the eyeglass lens.


Although a customer has the option of assembling their own system, Bosch has a standard sensor package that can be mounted on the system PCB:

  • The BHI260AB includes a programmable microcontroller, a 6-axis IMU, and preinstalled sensor fusion software.

  • The BMP388 is an absolute barometric pressure sensor.

  • The BMM150 is a magnetometer.

These sensors use very low levels of power, thus relieving some of the load on your connected device.

The IMU can detect all kinds of movements, for example, If you are in a complex situation, say jogging, running, walking, doing exercises — you’re turning around, you’re moving, there’s activity going on, sometimes you have your head or your hand in different positions. With the accelerometer, you can detect static and dynamic acceleration, you can see orientation in an earth gravity field and so on. Rotation can be measured by the IMU gyroscope. The sensor fusion software can incorporate the data from the IMU and magnetometer and provide precise and reliable orientation information.

Figure 3. The Bosch Smart Glasses Light Drive system displays just-in-time hands-free information in a minimalist format, making it ideal for applications such as navigation on bikes. (Image courtesy of ArturVerkhovetskiy /

The pressure sensor can sense changes in altitude with enough absolute accuracy, relative accuracy, and resolution, in the range of 10 to 30 cm, to detect steps if you are walking up the stairs or lifting your legs doing exercises.

The magnetometer can provide heading information while you are walking, running or riding a bike.


Figure 4. To limit power consumption, the BMA456 accelerometer, for example, accurately distinguishes between motion and no-motion, switching itself and the device to a low-power mode. This significantly extends the battery life of the entire system. (Image courtesy of Maridav/

Hearable devices are being increasingly used in fitness applications. “Bosch Sensortec’s many years of experience in the areas of signal processing and ultra-low power MEMS sensor design are key to helping manufacturers create the next generation of hearables,” said CEO Dr. Stefan Finkbeiner. They have developed a new variant of their high-performance BMA456 accelerometer that includes features optimized for hearable devices to be integrated in a single sensor. Accelerometers enable sensing for initiating voice assistant systems, head gesture control, body movement tracking, and more.

The new BMA456 accelerometer variant integrates hearable-specific gestures for intuitive user interactions such as tap, double-tap, and triple-tap. Thereby, the user can, for example, conveniently control playback, manage the volume, or accept and decline calls. All of these functions are carried out within the BMA456 itself, thus eliminating the need to wake up a power-hungry application processor. These features and its extremely low height of 0.65 mm make the BMA456 a perfect fit for truly wireless stereo (TWS) headsets and midrange hearables used for entertainment and in everyday life.

Another feature is power management. To limit power consumption, the BMA456 accelerometer accurately distinguishes between motion and no-motion, switching itself and the hearable device to a low-power mode. In addition, the accelerometer in combination with other sensors such as optical proximity, enables low-power in-ear and out-of-ear recognition that could instantly pause playback when the user removes the hearable from their ear and set the entire system into sleep mode.

The BMA456 also includes a low-power step detector and step counter specifically optimized for hearables. In combination with the sophisticated activity recognition feature that detects walking, running, and standing still, the BMA456 hearable variant is designed for sports and activity-tracking hearables that operate with smartphones or standalone.

Manufacturers can flexibly configure the default parameter sets of these features to improve the performance of their devices. The sensor’s low noise of 120 g√Hz, low offset of ±20 mg, and low TCO of 0.35 mg/°K further improve the accuracy of the device. Users thereby benefit from an intuitive user experience, accurate activity tracking, and extended battery life.

In addition, the BHI260AB, BMM150 and BMP388 can be integrated into hearables as well.

Going from Here

Hearables have been around for some time and seeables not so much. But both applications are on the cusp of a rapidly expanding market. While fitness monitors are growing more and more popular, the rapidly evolving ease of using smart eyeglasses and wireless earbuds are a big selling point. They are increasingly sophisticated, easier to use, and provide more information in unobtrusive ways than ever before.

This article was written by Ed Brown, Editor of Sensor Technology. For more information, visit here .